The present invention relates to transmissions for use in the power trains of motor vehicles, and more particularly to improvements in so-called automated transmissions which can be shifted into or from selected (such as neutral, reverse and forward) gears by so-called actuators in response to signals from one or more control units. As used herein, the term actuator is intended to denote a device which performs an action or outputs a signal in response to a signal from a computer or another suitable control unit. Still more particularly, the invention relates to improvements in automated transmissions wherein a gear selecting and/or shifting member (e.g., a rotary and axially movable member) receives or can receive motion from an axially shiftable output element of an actuator.
The power train of a motor vehicle normally comprises a prime mover (such as an internal combustion engine or a hybrid unit including a motor and a combustion engine), and a transmission which is installed in the power flow from the output element (such as a crankshaft or a camshaft) of the prime mover to the driven wheel or wheels of the motor vehicle. The transmission is shiftable into different gears to thus select the direction and/or the speed of movement of the vehicle. In other words, the transmission can establish a desired relationship between one or more prime mover parameters (such as the RPM of a rotary output element of an internal combustion engine) and one or more parameters (such as the speed and/or the direction of movement) of the motor vehicle. The ratio of the transmission can be changed by hand (e.g., by way of a conventional gear selecting and shifting lever) or automatically (e.g., by the aforementioned control unit and one or more actuators). For example, a manual or automated transmission can be shifted into neutral, into at least one reverse gear, and into one or more (e.g., an infinite number of) forward gears.
A manually engageable and disengageable or an automated torque transmitting system (such as a friction clutch) can be installed between the prime mover and the transmission or downstream of the transmission.
An automated transmission is disclosed, for example, in published German patent application Serial No. 43 20 353. This automated transmission can be operated by resorting to a source of a pressurized fluid medium, and its drawback is that the power train embodying such transmission cannot be caused to shift from normal operation to an emergency mode when the source of pressurized fluid is damaged or totally out of commission for whatever reason or reasons. The same holds true if actuators between a control unit and the automated transmission of the character disclosed in the aforementioned published German patent application become defective or totally disabled. The result is that the transmission cannot be shifted from a previously selected gear into a different gear, e.g., from reverse gear or a forward gear into neutral.